Pristine atmospheric condition over the Third Pole:An insight from levoglucosan records

Expanding urbanization and agricultural intensification across neighboring South Asia and East Asia have substantially threatened atmospheric condition over the Third Pole(TP)during the past few decades.Whether the atmospheric condition over the TP is still as clean as a representative of the regional background draws great concern.In this work,great differences in levoglucosan concentration within/above the atmospheric boundary layer height are revealed.Levoglucosan results support the hypothesis that atmospheric pollutants in the mid-troposphere over the TP are mainly affected by long-range transport,although there are some local biomass burning emissions in residential areas.In addition,levoglucosan concentration in the midtroposphere over the TP is at the same magnitude as marine and polar regions,but about 2–3 magnitudes lower than neighboring densely-populated Asian regions.With insights of levoglucosan records,this work therefore proves that the high-altitude TP still has largely pristine atmospheric conditions,and is one of the cleanest remote regions on the Earth.

NUMERICAL SIMULATION STUDY OF THE OCCURRENCE AND DEVELOPMENT OF A MID-TROPOSPHERIC CYCLONE OVER THE SOUTH CHINA SEA

In this paper,the processes of the occurrence and development of a mid-tropospheric cyclone (MTC hereinafter) over the South China Sea are successfully simulated,adopting the convective heating profile calculated from the ana- lysed data.And a series of numerical experiments show that the convective heating rate, especially its vertical profile, plays a key role in the occurrence,development and maintenance of the MTC.When there is highly concentrated convective heating in middle layer(400—450hPa),the MTC could occur and maintain for longer time.And the key to successfully predict the MTC by numerical model is to correctly specify the convective heating profile in the model.

AN ANALYSIS OF RECURVATURE AND DECAY OF THE TROPICAL CYCLONE ‘MADI’(2013) OVER THE BAY OF BENGAL

The track of tropical cyclone‘Madi’showed almost 180° turn around,while immediately after recurvature it decayed rapidly in the following 24 hours.Sea surface temperature(SST)analyses rule out confrontation with low SST as cause of weakening.At 0000 UTC of 9 December 2013 diabatic heating(DH),potential vorticity(PV)and vertical wind shear(VWS)were favourable for intensification.However,a dry area close to the system centre at mid-troposphere subsequently engulfed the middle strata and the mid-tropospheric relative humidity(MTH)drastically reduced on 0000 UTC of 10 December 2013.The MTH further reduced on 0000 UTC of 11 December 2013.Lack of moisture in mid-troposphere apparently caused a mutation within the structure causing a sudden decrease in elevation.As the system dried up,reduction in convection above 400 h Pa hindered latent heat release.PV above 400 h Pa decreased significantly.Eventually,there was a spurt of VWS at 1200 UTC of the 10December 2013.The opposite wind flow between lower level and upper level whisked away the top of the system to northeast.Under the influence of the net northeasterly flow in lower to middle troposphere,the miniature vortex recurved southwestward and the vertical distortion due to shear weakened the system into a depression.